I found two potential memory leaks which I fixed in the git version, so you can try again.
Another possibility, which is actually preferred, is to limit the size of the subject filed to a reasonable number. You can do that with following option
Format subject = 0, attribname, attribvalue, 80, 200
This shows the subject line with a width of 80 characters, but does only allow 200 characters to be entered there.